This invention relates to a method for controlling the operation of a multistage hydraulic machine and, more particularly, to a method for controlling and adjusting a load or water flow rate of water in a steady operating condition of a multistage hydraulic machine, generally a pump/turbine, in which all pressure stages are interconnected through return passages and the highest and lowest pressure stages are provided with movable guide vanes.
In a known multistage hydraulic machine in which all pressure stages are provided with runners and interconnected respectively through return passages, the operation or running control of the multistage hydraulic machine is done by controlling the flow condition of water passing the respective pressure stages in accordance with the adjustment of degrees of openings of guide vanes provided on the peripheries of the runners of the respective pressure stages. However, with the multistage hydraulic machine of the type described above, it is extremely difficult because of constructional limitations to provide guide vanes on the outer peripheries of the runners of the corresponding pressure stages and to control the opening or closing of the guide vanes by a guide vane control unit which is connected to the guide vanes, which provides a problem for practical use of the multistage hydraulic machine.
Taking the above problem into consideration, in the other controlling method the stationary guide vanes having a constant degree of opening are usually located on the outer peripheral surface of a runner of each pressure stage and the adjustment of the water flow rate and machine control operation are performed by open-close control of the inlet valve provided at an inlet portion of the multistage hydraulic machine. However, in this method, the water flow condition at the periphery of the runner of each pressure stage cannot be properly adjusted in response to the flow rate of water passing there, so that in low and high flow-rate ranges apart from design points, hydraulic performance lowers and the hydraulic machine is operated under lowered overall hydraulic performance.
In order to obviate defects or problems described above, there has also been proposed a controlling method in which movable guide vanes are provided for either one of the highest and lowest pressure stages and the flow rates of water can be adjusted by regulating the degree of opening of the movable guide vanes. However, in this controlling method, there remain problems such as vibrations, noises and cavitation caused at the operation in the low flow-rate range.
There has further been proposed a multistage hydraulic machine provided with movable guide vanes, the degrees of openings of which can be controlled, at the highest and lowest pressure stages for achieving stable and reasonable high hydraulic performance. The multistage hydraulic machine having the highest and lowest pressure stages provided with the movable guide vanes, the degrees of openings of which can be controlled, has a relatively complicated water flow passage in comparison with that of a single stage hydraulic machine and it is also necessary to accurately control the degrees of openings of the movable guide vanes, because of two movable guide vane assemblies at two pressure stages, at a time of load adjustment and control under a normal operation of the multistage hydraulic machine. In a point of this view, in a case where the adjustment of the degrees of openings of the movable guide vanes cannot be accurately performed, head ratio or distribution on the runners of the respective stages becomes nonuniform, which may cause the lowering of the hydraulic performance of the multistage hydraulic machine and generate cavitation, vibrations and noises at the lowest pressure stage as well as increasing of water pressure.